O3 System Research Articles

Magnetic Structure and Magnetotransport Properties of La0.7Sr0.3Mn1 – xNi x O3

La0.7Sr0.3Mn1 – xNi x O3 (0.12 ≤ x ≤ 0.35) compositions have been studied using neutron diffraction, magnetometry, and measurements of magnetotransport properties. At temperatures of 5–300 K, these compounds were found to have a rhombohedral crystal structure. The substitution of nickel for manganese has been shown to result in a decrease in the Curie temperature from 278 K (х = 0.12) to 60 K (х = 0.3); in this case, the spontaneous magnetization of the compositions decreases to zero (x = 0.33). The magnetoresistive effect for the semimetals with 0.12 ≤ x < 0.18 increases near the Curie temperature, whereas the magnetoresistance of semiconducting compositions with х ≥ 0.2 progressively decreases as the temperature increases. For compositions with х ≥ 0.25, an antiferromagnetic G-type component has been found by neutron diffraction, the Neel temperature of which reaches 260 K (at х = 0.35). The study of the La1–ySr y Mn0.65Ni0.35O3 (y ≤ 0.3) system showed that the content of ferromagnetic component decreases with increasing Sr content. It has been inferred that the antiferromagnetism of the compositions with х > 0.25 is due to the strong negative exchange interactions Ni2+–О–Ni2+ and Mn4+–О–Mn4+ and the absence of ionic order. The obtained data have been used to construct the magnetic phase diagram of the La0.7Sr0.3Mn1–xNi x O3 (0.12 ≤ x ≤ 0.35) system.

Specific Features of the Structure and Properties of High-Temperature Oxide Materials Based on Bismuth Sodium Titanate

Single-phase ceramic samples from the region of morphotropic phase boundary in the (1–x)(Na0.5Bi0.5)TiO3–xBaTiO3 and (1–y)[(Na0.5Bi0.5)TiO3–xBaTiO3]–yBi(Mg0.5Ti0.5)O3 systems, modified by low-melting LiF and 0.6NaCl–0.4LiF additives, have been prepared by solid-state synthesis. The effect of additives on the phase formation, structural parameters, and dielectric and ferroelectric properties of the ceramics has been studied. A decrease in the ceramic sintering temperature is found. A slight increase in the unit-cell volume upon modification of the ceramics under study by lithium fluoride and 0.6NaCl–0.4LiF additive is revealed. First-order ferroelectric phase transitions near 700–800 K have been observed. The prospects for improving the piezoelectric properties of modified ceramic samples are proved.

Global potential energy surface of ground state singlet spin O4.

A new global potential energy for the singlet spin state O4 system is reported using CASPT2/aug-cc-pVTZ ab initio calculations. The geometries for the six-dimensional surface are constructed using a novel point generation scheme that employs randomly generated configurations based on the beta distribution. The advantage of this scheme is apparent in the reduction of the number of required geometries for a reasonably accurate potential energy surface (PES) and the consequent decrease in the overall computational effort. The reported surface matches well with the recently published singlet surface by Paukku et al. [J. Chem. Phys. 147, 034301 (2017)]. In addition to the O4 PES, the ground state N4 PES is also constructed using the point generation scheme and compared with the existing PES [Y. Paukku et al., J. Chem. Phys. 139, 044309 (2013)]. The singlet surface is constructed with the aim of studying high energy O2-O2 collisions and predicting collision induced dissociation cross section to be used in simulating non-equilibrium aerothermodynamic flows.

Unfolding dielectric breakdown effects on energy storage performances of modified (Sr0.98Ca0.02)(Ti1‐xZrx)O3 ceramics

AbstractDielectric materials with large maximum polarization but small lossy hysteresis, high electrical breakdown, and postponed maximum polarization can store a large amount of electrical energy and are thus promising candidates for energy storage applications. In this work, a dielectric capacitor based on (Sr0.98Ca0.02)(Ti,Zr)O3 system achieved the elevated energy storage performances calculated from the polarization‐electric field hysteresis loops due to enhanced breakdown strength by Zr substitution. Dielectric relaxation could be ascribed to the appearance of the doubly ionized oxygen vacancies verified by activation energy. For the studied system, dielectric breakdown dominated for the enhancement of energy storage performances because of the difference of ferroelectric activity and cation stability between Zr and Ti ions. The optimal Zr‐modified composition exhibited better energy storage performances in contrast with pure (Sr0.98Ca0.02)TiO3, suggesting that they might be an emerging candidate for next‐generation high‐energy devices.

Nonlinear behavior of structural and luminescent properties in Gd(NbxTa1-x)O4 mixed crystals

Ceramic samples of gadolinium tantalo-niobate mixed crystals were obtained by the solid-state technique. The dependence of luminescence properties on the Nb/Ta ratio in the Gd(NbxTa1-x)O4 system is studied in the 5–450 K temperature range, including thermostimulated luminescence curves in the series of solid solutions. The relation of nonlinear behavior of light output with x variation to non-homogeneous distribution of Nb and Ta in solid solutions is discussed.

Preparation and Physical Chemistry Characterization of New Nanostructured Oxides Catalysts by Spray Pyrolysis Method for the Biodiesel Production

In this work were synthesized new catalysts of stoichiometries Sr0.8K0.2TiCu0.10O3, Sr0.7K0.3TiCu0.15O3 and Sr0.5K0.5TiCu0.25O3 by spray pyrolysis method. The synthesis conditions were optimized to obtain single phase powder of titanates of double perovskite structure, with an ultrasound vibration frequency of 1.3 MHz at 700 °C under air flow. The average crystallite size of the powders, determined by the Scherrer equation and using the Jade Plus 8 software, was at around 9 nm. The powder morphology was analyzed by scanning electron microscopy (SEM). The Sr0.5K0.5TiCu0.25O3 system showed particles with smooth surfaces, spherical and with smaller agglomerates than Sr0.8K0.2TiCu0.10O3, Sr0.7K0.3TiCu0.15O3 systems. This phenomenon suggests that the stoichiometry changes the aspect of the particle surface, which may influence in the catalytic activity. Thus, particles without roughening and smaller size can act as promising catalysts.

Impact of trace extrinsic defect formation on the local symmetry transition in spinel LiNi0.5Mn1.5O4−δ systems and their electrochemical characteristics

Many fundamental studies have been conducted on the electrochemical and electronic structures in transition metal cation-substituted LiNi0.5Mn1.5O4 systems.

Effects of sintering temperature on structure, magnetic and dielectric properties of La0.5Sr0.5Fe0.9Mn0.05Ti0.05O3 material

We have investigated structure, magnetic and dielectric of La0.5Sr0.5Fe0.9Mn0.05Ti0.05O3 (LSFMTO) system using ultrasonic mixing method. LSFMTO system is driven by 40 kHz frequency and calcinate process up to 750°C for 30 minutes. Then sintering process also carried out by systematic various of temperature 900 °C, 1000 °C, and 1100 °C respectively, as same time previously. Very interestingly, the LSFMTO system exhibits ferroelectric (La,Sr)(Fe,Mn,Ti)O3 and ferromagnetic SrFe12019 properties and minor phase La2O3 by XRD interpretation analyzation. We have also carried out the measurement of LSFMTO system using a systematic applied the external magnetic field from 0 to 1 T and the electric polarization from 0 to 50 kV/m . The hysteresis curve of LSFMTO system shows the electricty coercive (Ec) increases while the saturation polarization (Pc) and the remanent polarization are tendency constant at the magnetic strength of 0.12 T. We believed that our finding of LSFMTO system is potensial to multiferroic material as magnetic sensor application.

Structure, dielectric, and piezoelectric properties of K0.5Na0.5NbO3-based lead-free ceramics.

Lead-free ceramics based on the (1 − x)K0.5Na0.5NbO3–xBi(Zn0.5Ti0.5)O3 (KNN–BZT) system obtained via the conventional solid-state processing technique were characterized for their crystal structure, microstructure, and electrical properties. Rietveld analysis of X-ray diffraction data confirmed the formation of a stable perovskite phase for Bi(Zn0.5Ti0.5)O3 substitutions up to 30 mol%. The crystal structure was found to transform from orthorhombic Amm2 to cubic Pm3̄m through mixed rhombohedral and tetragonal phases with the increase in Bi(Zn0.5Ti0.5)O3 content. Temperature-dependent dielectric behavior indicated an increase in diffuseness of both orthorhombic to tetragonal and tetragonal to cubic phase transitions as well as a gradual shift towards room temperature. The sample with x ≈ 0.02 exhibited a mixed rhombohedral and orthorhombic phase at room temperature. A high-temperature X-ray diffraction study confirmed the strong temperature dependence of the phase coexistence. The sample with the composition 0.98(K0.5Na0.5NbO3)–0.02(BiZn0.5Ti0.5O3) showed an improved room temperature piezoelectric coefficient d33 = 109 pC/N and a high Curie temperature TC = 383 °C.

Low-temperature sintered Li2(MnxTi1−x)O3 microwave dielectric ceramics with adjustable τf

B2O3–Bi2O3–SiO2–ZnO (BBSZ) glass-modified Li2(Mn[Formula: see text]Ti[Formula: see text])O3 ceramics were fabricated via a solid-state reaction route. Pure phase and dense crystal morphology were obtained at 900[Formula: see text]C. Suitable amount of Mn[Formula: see text]-ion substitution could adjust the [Formula: see text] value of the Li2(Mn[Formula: see text]Ti[Formula: see text])O3 system to near zero. Among all of the Li2(Mn[Formula: see text]Ti[Formula: see text])O3 samples, the sample with x = 0.9 (marked as BL9 in this paper) possessed good microwave dielectric properties: [Formula: see text] = 18, Q × f = 14,056 GHz (9.58 GHz) and [Formula: see text] = (+)2.43 ppm/[Formula: see text]C. It is suggested that the Li2(Mn[Formula: see text]Ti[Formula: see text])O3 ceramic with BBSZ glass is a suitable low-temperature co-fired ceramic (LTCC) candidate for microwave applications.

A highly sensitive chemical gas detecting device based on N-doped ZnO as a modified nanostructure media: A DFT+NBO analysis

We presented a density functional theory study of the adsorption of O3 and NO2 molecules on ZnO nanoparticles. Various adsorption geometries of O3 and NO2 over the nanoparticles were considered. For both O3 and NO2 adsorption systems, it was found that the adsorption on the N-doped nanoparticle is more favorable in energy than that on the pristine one. Therefore, the N-doped ZnO has a better efficiency to be utilized as O3 and NO2 detection device. For all cases, the binding sites were located on the zinc atoms of the nanoparticle. The charge analysis based on natural bond orbital (NBO) analysis indicates that charge was transferred from the surface to the adsorbed molecule. The projected density of states of the interacting atoms represent the formation of chemical bonds at the interface region. Molecular orbitals of the adsorption systems indicate that the HOMOs were mainly localized on the adsorbed O3 and NO2 molecules, whereas the electronic densities in the LUMOs were dominant at the ZnO nanocrystal surface. By examining the distribution of spin densities, we found that the magnetization was mainly located over the adsorbed molecules. For NO2 adsorbate, we found that the symmetric and asymmetric stretches were shifted to a lower frequency. The bending stretch mode was shifted to the higher frequency. Our DFT results thus provide a theoretical basis for why the adsorption of O3 and NO2 molecules on the N-doped ZnO nanoparticles may increase, giving rise to design and development of innovative and highly efficient sensor devices for O3 and NO2 recognition.

Mössbauer studies of spinellides of Mg(FeXCr2-X)O4 system obtained by the hydroxide co-precipitation method

To establish regularities in formation of the magnetic microstructure in magnesium ferrite-chromites by the method of co-precipitation of hydroxides from chlorides of corresponding salts, ferrite spinels were synthesized with Mg(Fe x Cr 2-x )O 4 composition. It was found by the method of X-ray diffraction analysis that the resulting spinel occupies an intermediate position between normal and inverse spinels. Substitution of chromium for a part of trivalent iron ions in the spinel phases leads to normalization of the spinel structure. The magnetic microstructure of the resulting samples, distribution of iron among sublattices and presence of Fe 2+ ions were investigated by the method of Mossbauer spectroscopy. It was established that the magnetically ordered phase is only present in samples with x>1.6. Due to the non-high sintering temperature, low symmetry of the near surrounding and continuous distribution of effective magnetic fields on the Fe 3+ nuclei were observed in the samples. Analysis of the results of Mossbauer and X-ray structural studies has shown deviation of the real near surrounding of the iron ion from the most probable surrounding. No Fe 2+ ions were detected by the Mossbauer method in these samples. There is a good agreement in the relation between population of the iron ions among octahedral and tetrahedral sublattices (2.0) found by methods of X-ray and Mossbauer analysis. The obtained information confirms significant dependence of the properties of ferrite-spinels on the features of synthesis and shows necessity of checking the sample characteristics during changes or modifications in the production methods.

Enhanced degradation and mineralization of 4-chloro-3-methyl phenol by Zn-CNTs/O3 system

A novel zinc-carbon nanotubes (Zn-CNTs) composite was prepared, characterized and used in O3 system for the enhanced degradation and mineralization of chlorinated phenol. The Zn-CNTs was characterized by SEM, BET and XRD, and the degradation of 4-chloro-3-methyl phenol (CMP) in aqueous solution was investigated using Zn-CNTs/O3 system. The experimental results showed that the rate constant of total organic carbon (TOC) removal was 0.29 min−1, much higher than that of only O3 system (0.059 min−1) because Zn-CNTs/O2 system could generate H2O2 in situ, the concentration of H2O2 could reach 156.14 mg/L within 60 min at pH 6.0. The high mineralization ratio of CMP by Zn-CNTs/O3 occurred at wide pH range (3.0–9.0). The increase of Zn-CNTs dosage or gas flow rate contributed to the enhancement of CMP mineralization. The intermediates of CMP degradation were identified and the possible degradation pathway was tentatively proposed.

Treatment of Landfill Leachate Reverse Osmosis Concentrate from by Catalytic Ozonation with γ-Al2O3

Abstract To develop a technology for the degradation of the toxic and refractory pollutants contained in landfill leachate reverse osmosis (RO) concentrate, a γ-Al2O3/O3 system was set up in this study. Landfill leachate RO concentrate was rejected from RO of biologically pretreated raw landfill leachate. First, its key operational parameters, including γ-Al2O3 dosage, ozone dosage, reaction temperature, treatment time, and initial pH value, were optimized through single-factor experiments. Under the optimal conditions, the chemical oxygen demand (COD) (70%) and color (100%) removal efficiencies could be obtained by the γ-Al2O3/O3 process. Meanwhile, the ratio of biochemical oxygen demand (BOD5) to COD (B/C ratio) was enhanced from 0.01 to 0.2, which suggests that its biodegradability was improved to some extent. Decomposition or transformation of organic pollutants in landfill leachate RO concentrate was analyzed by ultraviolet-visible spectroscopy, excitation–emission matrix fluorescence spectroscopy, a...

Dielectric, ferroelectric and piezoelectric properties of (Ba0.98−xSrxCa0.02) (Ti0.95Zr0.05)O3 lead-free ceramics

Piezoelectric compositions associated with the chemical formula (Ba0.98−xSrx Ca0.02)(Ti0.95Zr0.05)O3 where x = 0, 0.05, 0.10 and 0.15, were synthesized successfully via solid-state reaction route. The dielectric, ferroelectric, piezoelectric and strain properties of the ceramics of these compositions were studied. X-ray diffraction studies confirmed the presence of pure tetragonal structure and the cell volume was found to decrease with the increase in Sr content. Scanning electron microscopy showed increase in grain size for Sr doped samples when compared to undoped ceramics. Interestingly, the sample with x = 0.10 mol of Sr content exhibited excellent piezoelectric properties. The polarization and strain behaviour for the aforementioned sample showed high piezoelectric strain of 0.22% at 40 kV/cm. The remnant polarization of 13.45 μC/cm2 associated with high piezoelectric coefficient (d33) of 320 pC/N were obtained for the ceramic with x = 0.10 mol of Sr content. These results confirmed that the (Ba0.88 Sr0.10Ca0.02)(Ti0.95Zr0.05)O3 system is a promising lead-free high piezoelectric strain material for piezoelectric based device applications.

Large piezoelectric responses of Bi(Fe,Mg,Ti)O3-BaTiO3 lead-free piezoceramics near the morphotropic phase boundary

The (1-x)Bi1+y(Fe0.96Mg0.02Ti0.02)O3-xBaTiO3 (abbreviated as B1+yFMT-xBT) system was designed to explore the morphotropic phase boundary (MPB) separating rhombohedral (R) and tetragonal (T) phases, and the mechanism of performance enhancement. The phase structure of samples was discreetly investigated by X-ray diffraction, and Rietveld refinement results of the XRD data revealed that the B1+yFMT-xBT ceramics consist of an R phase at x = 0.24, two R and T phases at 0.26 ≤ x ≤ 0.32, and a single T phase at x = 0.34. Because of the MPB and the improvement of resistivity with adding excess Bi compensation, excellent piezoelectric properties of d33 = 198 pC/N and kp = 30.9%, as well as high Curie temperature TC = 497 °C were achieved in the B1+yFMT-xBT system at x = 0.30 and y = 0.02. Here, the large d33 = 198 pC/N which is the maximum value for the BF-BT-Bi(Mg,Ti)O3 system so far, and high TC = 497 °C suggest that Bi(Fe,Mg,Ti)O3-BaTiO3 ceramics have good prospects in high-temperature piezoelectric devices.

Potential energy surfaces of quintet and singlet O4.

We present global ground-state potential energy surfaces for the quintet and singlet spin states of the O4 system that are suitable for treating high-energy vibrational-rotational energy transfer and collision-induced dissociation in electronically adiabatic, spin-conserving O2-O2 collisions. The surfaces are based on MS-CASPT2/maug-cc-pVTZ electronic structure calculations with scaled external correlation. The active space has 16 electrons in 12 orbitals. The calculations cover nine kinds of geometrical arrangements corresponding to dissociative diatom-diatom collisions of O2, geometries corresponding to O3-O, geometries identified by running trajectories, and geometries along linear synchronous transit paths. The global ground-state potential energy surfaces were obtained by a many-body approach with an accurate O-O pairwise interaction and a fit of the many-body interaction to 12 684 electronic structure data points for the singlet and 10 543 electronic structure data points for the quintet. The many-body fit is based on permutationally invariant polynomials in terms of bond-order functions of the six interatomic distances; the bond-order functions are mixed exponential-Gaussian functions.

Study of phase evolution and dielectric properties of Sn-doped barium titanate

The reaction of barium carbonate (BaCO3) with titanium dioxide (TiO2) was studied by simultaneous thermogravimetric and differential scanning calorimetric analysis up to 1000°C. Based on the results of thermal analysis, three compositions (x = 0·00, 0·05 and 0·15) of the BaTi1−x Sn x O3 system were synthesized by calcination at 1000 and 1100°C and sintering at 1350°C. The effect of calcination temperature on the phase formation of these samples was investigated by recording X-ray diffraction patterns. The single-phase tetragonal barium titanate (BaTiO3) was obtained at 1100°C. Analysis of the X-ray diffraction studies of samples x = 0·05 and 0·15 confirmed that the formation of single-phase solid solutions BaTi0·95Sn0·05O3 and BaTi0·85Sn0·15O3 takes place by way of formation of barium titanate and barium stannate (BaSnO3) phases and a reaction between them at temperature &gt;1100°C. The percentage formation of single-phase solid solution and the lattice parameter increase with increasing calcination temperature. The phase purity of the obtained powders was also examined using Fourier transform infrared spectroscopy. Morphological and compositional analyses of the samples were performed using scanning electron microscopy and energy-dispersive X-ray analysis, respectively. Dielectric constant and dissipation factor of the samples were measured in the temperature range of 100 to 200°C and frequency range of 50 Hz–2 MHz.

Magnetocaloric effect and influence of Fe/Cr disorder on the magnetization reversal and dielectric relaxation in RFe0.5Cr0.5O3 systems

We have investigated the structural, magnetic, and dielectric properties of RFe0.5Cr0.5O3 (R = Nd, Sm, Gd, and Y) compounds. Both structure and magnetic analyses show a Fe/Cr cation disorder, which results in the existence of Fe-rich and Cr-rich clusters. The competition between the moments of the two clusters gives rise to the R-dependent temperature induced magnetization reversal. Interestingly, we also find that the charge carrier hopping in the two clusters leads to two sequential dielectric relaxations in all the samples. In addition, giant magnetocaloric effect with a magnetic entropy change reaching ∼29.2 J/kg K was observed with R = Gd.

Mechanochemical synthesis, crystal structure and ion conduction in the Gd2Hf2−x Ti x O7 system

This work describes the mechanochemical synthesis, structural characterization and electrical properties of an interesting group of novel ionic conductors, with general formula Gd2(Hf2−x Ti x )2O7. Different compositions in this system (x = 0, 0.4, 0.8, 1.2, 1.6 and 2) were obtained at room temperature, via a mechanochemical reaction between the corresponding elemental oxides, and characterized by using XRD, Raman spectroscopy and SEM. The XRD structural analysis by the Rietveld method revealed that all the Hf-containing compositions show a disordered fluorite-like structure instead of the expected pyrochlore-like atomic ordering, and the cation size mismatch criteria for pyrochlore stability. Increasing Ti content promotes a phase transformation to the pyrochlore structure with post-milling thermal treatments, which takes place in all samples on annealing at 1200 °C, except for Gd2Hf2O7. These results were confirmed by Raman spectroscopy, which also suggests that the x = 0.4 sample has the highest degree of oxygen disorder in the system and that this disorder decreases with increasing Ti4+ content. Finally, all samples show the pyrochlore structure on firing at 1500 °C. Activation energies E dc for oxygen migration were determined by using impedance spectroscopy and found to be within the ~0.9–1.2 eV range, whereas conductivity σ dc values at 700 °C vary from 1.12 × 10−6 to 2.75 × 10−4 S cm−1, with decreasing conductivity as Ti4+ content increases.